The present invention is directed to a switching or connecting network, and in particular to a remotely reconfigurable switching network for a telephone system.
Remotely controllable xe2x80x9crealxe2x80x9d cross-connect switching networks such as the Remote Cable Pair Switching System (RECAPSS) or the Remote Pair Cross Connect System (REPACCS) manufactured by Remote Switch Systems, Inc. or the Smart-MDF product manufactured by OKI are well known and widely used as an interface to establish connections between input terminals and output terminals in a predetermined manner from a remote location. An example of a conventional xe2x80x9crealxe2x80x9d cross-point switching network is shown in FIGS. 1a and 1b. The network includes two cross-point switches 100, 150 each having N input lines running horizontally through the switch and N output lines running vertically through the switch. Switching elements 110, 160 represented by the small circles at the intersections of the input and output lines are placed at the nodes, that is the intersections or cross-points of the horizontal and vertical lines. Normally, the switching elements are in an open state with no connection between the input and output lines. A desired connection between an input and an output line may be formed by remotely controlling the switching element at the node where the two lines intersect. In this manner, any prescribed connection between input and output lines may be realized by remotely accessing the respective switching element.
xe2x80x9cRealxe2x80x9d cross-connect switching networks are commonly employed in the telecommunications industry wherein telephone subscribers are allowed to switch between local exchange carriers. Switching local carriers may require a physical rewiring or cross-connection between the subscriber""s loop owned by the incumbent local exchange carrier (ILEC) and the network facilities of the competitive local exchange carriers (CLECs). In one specific application the switching network may be used to provide a particular type of service, for example, Asymmetric Digital Subscriber Loop (ADSL) service, to an existing plain old telephone service (POTS) subscriber loop served out of a central office. To provide additional services to the subscriber loop adjunct equipment 115 such as ADSL modems, line cards, diplexers and filters may be installed between the two switches 100, 150.
By way of example, in FIG. 1 the adjunct equipment 115 is installed only at output line #1. It should be noted, however, that additional adjunct equipment may be added to other output lines as the demand for such services among subscribers increases. The first switch 110 is used to connect a given input terminal of a subscriber requesting the particular service provided by the adjunct device 115 to output line #1. The signal from output line #1 is then split off and passes through the adjunct equipment 115 which provides the additional service, for example, ADSL service. In addition, the signal from output line #1 also passes through the second switch 150 that returns the signal lines to their original arrangement. This xe2x80x9crealxe2x80x9d cross-connect switching network is disadvantageous in that each switch requires a relatively large number of switching nodes which are expensive. In particular, an Nxc3x97N switch has N2 switching nodes, for example, in a 2xc3x972 switch there are 4 switching nodes, in a 4xc3x974 switch there are 16 switching nodes, and in an 8xc3x978 switch there are 64 switching nodes.
V. E. Benes developed a switch described in xe2x80x9cOptimal Rearrangeable Multistage Connecting Networksxe2x80x9d, The Bell System Technical Journal, pp. 1641-1656 (July 1964), incorporated herein by reference, that requires fewer switching nodes than a xe2x80x9crealxe2x80x9d cross-connect switch. The basic component of a Benes switch is a beta network, as shown in FIGS. 2a and 2b, including two relays, such as two double pole double throw (DPDT) latching relays. Beta network 200 has two input lines, xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d, and two output lines xe2x80x9ccxe2x80x9d, xe2x80x9cdxe2x80x9d, wherein the input and output lines are switchable between two states. In the first state shown in FIG. 2a input lines xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d are directly connected to output lines xe2x80x9ccxe2x80x9d, xe2x80x9cdxe2x80x9d, respectively. In the second state shown in FIG. 2b, the lines are crossed, that is, input lines xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d are connected to output lines xe2x80x9cdxe2x80x9d, xe2x80x9ccxe2x80x9d, respectively. It is clear that since two states can be achieved using a single beta network (Benes node) the number of nodes in the switch is reduced.
A plurality of beta networks may be arranged to form a Benes switch. By way of example, an 8xc3x978 Benes switch 200 is shown in FIG. 2c. The 8xc3x978 Benes switch includes 20 beta networks, as compared to 64 crosspoints in the prior art cross-connect switch. The 2xc3x972 beta network is grown into a 4xc3x974 Benes switch with three-stages of beta networks by duplicating the original switch and positioning the duplicated switch below the original switch. Specifically, the original 2xc3x972 switch 210U is duplicated to form a lower switch 210L positioned below the upper switch. Then the appropriate number of additional input and output beta networks 215a-215d are connected to the inputs and outputs of the upper and lower switches. Each additional beta network has one output connected to the upper switch 210U and the other output connected to the lower switch 210L to create the 4xc3x974 Benes switching network 230 with three stages of beta networks.
Similarly, an 8xc3x978 Benes switching network may be created following the same procedure described above with respect to building the 4xc3x974 Benes switch, except that the original or upper switch is now the 4xc3x974 switch 230, instead of the 2xc3x972 switch 210U. Specifically, the 4xc3x974 Benes switch 230 is duplicated to form a lower switch 250 positioned directly below the upper switch. Then the appropriate number of additional input and output beta networks 205a-205h are connected to the inputs and outputs of the upper and lower switches. Each additional beta network 205a-205h has one output connected to the upper switch 230 and the other output connected to the lower switch 250 to form an 8xc3x978 Benes switching network with five stages of beta networks. By following these basic steps the Benes network may be expanded as desired.
Benes switches may also be used to interconnect input and output terminals in order to provide additional services to predetermined subscribers. In a configuration similar to that described above with respect to cross-point switches, one or more adjunct devices may be disposed between two Benes switches. Specifically, the switching network includes a first Benes switch for selecting a particular subscriber to receive the additional service, an adjunct device connected to at least one output line of the first Benes switch to provide the necessary additional service capabilities depending on subscriber demand, and a second Benes switch connected to the output lines of the first Benes switch to return the signal lines to their original arrangement. This switching network is disadvantageous in that it still requires two Benes switches, each including a relatively large number of Benes nodes, and thus is relatively expensive to manufacture.
It is therefore desirable to develop a remotely accessible switching network that may be reconfigured to provide adjunct equipment specifically tailored to satisfy subscriber demand for a particular service while minimizing the number of switching nodes.
The present invention is directed to a remotely reconfigurable switching network. In a preferred embodiment the remotely reconfigurable Nxc3x97N switching network includes an Nxc3x97N Benes switch having a plurality of stages of beta networks. The Benes switch is separated into a left half section and a right half section, with one of the sections having one less stage of beta networks than the other section. An additional stage of beta networks is connected to the section having one less stage of beta networks so that the stages of beta networks in the left and right half sections mirror one another. In addition, at least one attachment device is interposed between the left and right half sections.
Furthermore, an exemplary embodiment of the present invention is a method for manufacturing a remotely reconfigurable switching network as described in the preceding paragraph. An Nxc3x97N Benes switch, including a plurality of stages of beta networks, is separated into a left half section and a right half section, with one of the sections having one fewer stage of beta networks then the other section. Then an additional stage of beta networks is connected to the section having one less stage of beta networks so that the left and right half sections mirror one another. At least one attachment device is then inserted between the mirrored left and right sections.